From among methods of forming a thin film, e.g., a silicon oxide (SiO2) film or a silicon nitride (Si3N4) film, on a semiconductor wafer (hereinafter referred to as a “wafer”), there is known a method that makes use of plasma obtained by converting a process gas, such as a silicon-containing raw material gas or a reaction gas (an oxidizing gas or a nitriding gas) reacting with the raw material gas, to form plasma. Examples of film formation methods include CVD (Chemical Vapor Deposition) and ALD (Atomic Layer Deposition). In case of the CVD method, a raw material gas and a reaction gas are converted to plasma and caused to react with each other in a vapor phase. A reaction product generated by the reaction is deposited on a wafer. On the other hand, in the ALD method, plasma obtained by the raw material gas and plasma obtained by the reaction gas are alternately supplied to the wafer, thereby alternately performing an adsorption of a silicon component onto a surface of the wafer and a reaction of the silicon component on the surface of the wafer.
As an example of a film formation apparatus for use in the film formation method, there is available an apparatus in which a table unit for placing, e.g., a wafer, thereon is installed as a lower electrode within a processing vessel and in which a gas shower head used as an upper electrode is disposed to face the table unit. Plasma of a process gas is obtained by supplying a process gas into the processing vessel and applying a high-frequency power having a frequency of, e.g., 13.56 MHz, to one of the table unit and the gas shower head.
In case where a recess such as a hole or a groove is formed on the surface of the wafer, if the recess has an aspect ratio of several tens or several hundreds, it becomes difficult to satisfactorily form a film on inner wall surfaces of the recess. In other words, thin films formed on the inner wall surfaces of the recess become smaller in thickness or poorer in quality than thin films formed on a horizontal surface of the wafer (a bottom surface of the recess and the upper surface of the wafer). There is available a conventional apparatus in which a dipole ring magnet is disposed outside a processing chamber. However, the conventional apparatus is outdated in terms of the aforementioned problems.